1. Field of the Invention
This invention relates to novel ply-twisted yarns which may be used as pile yarn in a carpet to improve the carpet's texture retention. The yarns are composed of a blend of polyamide and/or polyester fibers and non-melt compatible polyolefin fibers.
2. Description of the Related Art
A large portion of carpets used in residences in the United States are known as cut pile saxony carpets. In saxony carpets, pile yarn is inserted into a backing material as loops which are cut to form vertical tufts. The tufts are then evenly sheared to a medium-length height. The cut ends of the tufts are referred to as the tuft tips. Generally, there are two different styles of saxony carpets: 1) a straight-set style in which the tufts are straight and substantially perpendicular to the plane of the carpet face, and 2) a textured style in which the tufts have varying degrees of curl.
Staple fiber, which refers to cut lengths of fiber from continuous filaments, may be processed into yarn suitable for saxony carpets by techniques known in the art. Generally, such techniques involve first combing crimped staple fiber in a carding machine to form sliver which is a continuous strand of loosely assembled fibers without twist. The sliver is then drafted on a drafting machine to improve its thickness uniformity and subsequently spun and twisted on a spinning machine to form singles twisted yarn. The singles twisted yarn may then be twisted with other singles twisted yarn(s) to form a ply-twisted yarn. Finally, the ply-twisted yarn is subjected to a heat-setting operation where the twist in the yarn is heat-set, thus making the yarn suitable for tufting.
It is important that the staple spun yarn have a high degree of thickness uniformity. The thickness uniformity of the staple spun yarn not only affects the quality of the finished carpet, but it also affects any subsequent processing steps. For instance, staple spun yarns with poor uniformity have a high number of thick and thin sections which greatly weaken the yarns, causing frequent fiber breaks during the ply-twisting phase. One object of the present invention is to produce a staple spun yarn having a high degree of thickness uniformity.
Secondly, the perceived value of saxony carpets is dependent upon several factors including carpet bulk and carpet "texture retention." By the term, "texture retention" as used herein, it is meant the ability of the carpet to retain its original tuft definition after being subjected to traffic. It is known that carpet bulk can be improved by increasing the face weight of the carpet or by increasing the crimp imposed on the staple fiber. However, carpet face weight is directly proportional to the carpet's total production cost. Furthermore, highly crimped staple fiber can create processing problems, especially during the carding operation. Another object of this invention is to produce yarns which may be tufted into carpets to provide good carpet bulk in such a manner that the above problems are avoided.
When saxony carpets are new, they have a pleasing texture. The bulked yarns which form the tufts provide firmness and body to the carpet. The ply-twist in the individual tufts allow for good tuft definition which gives the carpet a uniform and sharp appearance. Each tuft appears distinctly separate from neighboring tufts. However, when the carpet is subjected to a high degree of traffic, the tufts begin to untwist. This loss of twist causes the tuft tips to splay open. The individual filaments of one tuft tend to mingle with filaments of adjacent tufts giving the carpet a matted appearance and loss of texture. A still further object of this invention is to produce yarns which will impart improved texture retention to carpets.
Those skilled in the art have considered different ways for improving carpet texture retention. One method involves increasing the number of twists in the ply-twisted yarn. However, increasing the twist decreases carpet bulk and increases yarn production costs.
In other instances, yarns composed of a mixture of base fibers and potentially adhesive binder fibers may be prepared. Upon heat treatment, these binder fibers are activated and adhere to the base fibers in such a manner that the base fibers are bonded together. As mentioned in published UK Patent Application 2,205,116, the binder fibers may be bicomponent fibers in which one component of the fiber melts and becomes adhesive at a lower temperature than the other component in the fiber, or the binder fibers may be single component fibers in which the melting temperature is similar throughout the fiber. These binder fibers may also melt to such a degree that they substantially lose their identity as fibers, as described in published European Patent Specification 324,773. The above-described binder fibers may be referred to as "melt compatible" binder fibers, since the binder fibers have a chemical affinity with the base fibers and upon melting adhere to the base fibers.
The present invention provides a new yarn composed of a blend of polyamide and/or polyester fibers and "non-melt compatible" polyolefin fibers. By the term "non-melt compatible" as used herein, it is meant that upon heat activation, the polyolefin fibers will melt and adhere to other molten polyolefin fibers, but there is no adhesion between the polyolefin fibers and polyamide or polyester fibers. It has been found that these yarns have a high degree of thickness uniformity and provide good carpet bulk and improved texture retention.